Electron



Jan. 24, 1956 M. J. ZUNJCK ELECTRONEMITTER Filed March 13, 1952 Mun gmMN m W H m2 IIU I L E 0. Mwm

.l-Illlll] United States Patent 2,732,510 ELECTRON EMITIER Michael J.Zunick, Greenfield, Wis., assignor to General Electric Company, acorporation of New York Application March 13, 1952, Serial No. 276,313

' 12 Claims. c1, 313-37 The present invention relates in general toelectronics, and has more particular reference to electron emitters, theinvention pertaining especially to an improved support structure forfilaments of the sort commonly employed as electron emitting cathodes inelectron flow devices, such as X-ray generating tubes and the like.

X-ray generating tubes commonly comprise an anode and an electronemitting cathode element enclosed in a sealed and evacuated envelope,X-rays being generated at the anode as the result of impingement thereonof electrons emitted by the cathode element. The electron emittingelement is commonly mounted in a cathode structure embodying a cupadapted to aid in directing, toward the anode, electrons emitted by thecathode element. Such cathode structures have comprised a multiplicityof components, secured together, as by means of screw fasteningelements, and hence necessarily formed with threaded sockets forreceiving such elements. As a consequence, conventional supportstructures for electron emitters have been relatively expensive anddiflicult to assemble. Furthermore, the formation of threaded fasteningelements and corresponding threaded sockets in the components to bejoined, as well as the application of threaded elements in positionsecuring components together, commonly results in the production ofsmall metal particles, scraped or otherwise detached or loosened fromthe components of the structure, which, if accidentally allowed toremain in situ, may deleteriously affect the operation of an elec-' tronflow device .in which the emitter and its support struc ture areassembled. Such conventional support structures, of course, requiremanual assembly of the components, entailing undesirable handlingthereof during the assembly operations.

An important-object of the present invention is to pro,- vide animproved support structure for electron emitters,

comprising a minimum number of componentparts of relatively simple,inexpensive form and adapted to facilitate the assembly of the supportstructure at low cost.

Another important object is to provide a support structure for electronemitters embodying parts adapted for automatic assembly, as by applyingthe parts in a suitable jig, thereby minimizing the necessity ofhandling the parts during the assembly operation withconsequentreduction of handling contamination thereof.

Another important object resides'in providing a support structure of thecharacter mentioned having a minimum number of component parts adaptedto be secured together by welding, thereby avoiding the employment offastening screws and inhibiting the formation of loose metallicparticles in the support structure.

Another important object is 'to provide a structure of the charactermentioned'including a component comprising a cathode cup element havinga transverse groove formed in a face thereof :and channels orducts'communieating the bottom of the groove with the opposite face ofthe cup .element, and including stem supporting means located in seatsformed in said ducts for accurately locating and securing emittersupporting stems in said ducts.

Another important object is to provide improved means for mounting andinsulating an emitter support stern in a cathode cup element of thecharacter mentioned; a further object being to employ a block ofsuitable insulating material sized to fit snugly in a seat formed in thecup element, the block being formed with a support channel therein andsized to snugly receive an emitter support stem in accurately mountedposition in the cup element.

Another important objectis to employ'a formed block of insulatingmaterial comprising magnesium oxide, lava, glass, porcelain, or thelike, for mounting an emitter support stem in a cathode cup structure; afurther important object being to provide improved means for mountingand retaining the block of insulation in mounted position on the cathodecup element, saidmeans comprising a shelllike housing adapted to retainthe block in operative position to support and insulate an emittercarrying stem mounted therein, even though said block may become crackedin service. I

Another important object resides in the provision of improved means formechanically and electrically connecting an electron emitting filamenton a support stem.

Another important object is to provide improved and simplified meanswhereby a filament support stem may be mounted and secured in preciselyadjusted position in a stem supporting member, such as a cathode cupelement.

Another important object resides in providing a cathode structure of thecharacter mentioned including improved means for mounting the structurein rigid fashion on a mounting base adapted to form a portion of theevacuated envelope of an electron flow device, to thereby provide thecathode structure and its mounting base as a sub-assembly unit adaptedfor incorporation with envelope means, in building an electron flowdevice embodying said cathode structure in operative position therein.

The foregoing and numerous other important objects, advantages, andinherent functions of the invention will become apparent as the same ismore fully understood from the following description, which, taken inconnection with the accompanying drawings, discloses preferredembodiments of the invention.

Referring to the drawings:

Fig. 1 is a diagrammatic view of an electron flow device including acathode structure embodying the present invention;

Fig. 2 is an elevation view, partially sectionalized, showing astructure embodying the invention;

Figs. 3, 4 and 5 are sectional views taken substantially along ,thelines 3.-3, 4-4 and 5-5 in Fig. 2;

Fig. 6 is a sectional view showing a modified arrangement embodying theinvention;

Fig. 7 is a sectional view taken substantially along the line 7-7 inFig. 6;

Fig. 8 is a greatly enlarged view of the filament connected end of afilament support stem forming part of the structure shown in Figs. 2 and3 and Fig. 9 is an enlarged sectional view through a stem insulating andsupporting device forming a part of the structure shown in Figs. 2 and3.

To illustrate the invention thedrawings show electron emission meanscomprising a cathode structure C of a sort well adapted for use inelectron flow devices, such as an X-ray generating tube T. As shown, thetube comprises an anode A and the cathode structure C enclosed withinand supported on a sealed and evacuated envelope E, which may beof anydesired or preferred form and construction. X-ray generating devicesoperate as such in response to impingement on the anode of electronsemitted by the cathode, such electronic impingement resulting in thegeneration of X-rays at the anode, whence the enclosing envelope.

Metallic filaments are commonly employed as electron emitters 'inelectron fiow devices, such filaments 'be'ing electrically excitable,for electron emission therefrom, as by the passage of electrical currenttherethrough, from a power source located outwardly of the envelope ofthe device. Electrons emitted by an energized filament are commonlycaused to travel toward and to impinge upon the anode of the deviceunder the influence of an electron driving potential applied between thefilament and the anode, as .tlrom a suitable source of electrical poweralso disposed outwardly of the envelope. In such electron fiow devices,therefore, it is necessary to provide for mounting the electron emittingfilament Within the enclosing envelope, and .to provide for electricallyconnecting the filament not only with an external source of filamentenergizing power, but also with a suitable external power source forapplying electron driving potential bctween the anodeand cathodeof thedevice.

The present invention provides an improved .rnounting structure forsupporting an electron emission filament in operative position withinthe sealed envelope of an electron fiow device, the structure alsoaffording means for electrically connecting the supported filament withelectrical power sources located outwardly of the envelope of the devicein which the structure is or may be assembled for use.

As shown 'in the drawings, the electron emission means of the presentinvention comprises an electron emitting filament 11 and a supportstructure '12 for mounting the filament'li within the sealed envelope ofan electron flow device. The support structure 12 comprises a preferablycylindrical block 13 of any suitable material, such as steel, said blockhaving an outwardly opening slot or groove 14 formed in its front end,the groove 14, in 'the illustrated embodiment, extending diametricallyand trans verscly of the block 13 and opening at the opposite sidesthereof, thereby facilitating the formation of the groove by a simplemilling operation transversely across the front face of the block. Theblock 13 may also be formed with a pair of parallel, spaced apart,preferably cylini drical channels 15 and 15, said channels each openingat one end upon the bottom of the groove 14, the opposite ends of "thechannels opening into enlarged cavities 16 and 16' formed in'and openingoutwardly of the rear face of the block.

The filament 11 is supported in the groove 14 with the axis of thefilament lying substantially in the medial plane of the groove and at apredetermined elevation between the bottom and open top of the groove,the opposite ends of the filament being mechanically and electricallyconnected on mounting stems 17 and 17', of suitable electricalconducting material such as molybdenum, supported on the block 13 inposition extending coaxially with respect to the channels 15 and 1'5. Inthat connection, the stems 17 and 17' maybe formedwith tapered endportions '13 and means, extending and secured in the seats 16 and 16',is provided for mountingthe stems 17 and 17' in position on the block'13 presenting the tapered end portions 18 of the stems Within thechannels 15 and 15', the filament 11, atthe opposite ends thereof, beingformed with mounting extensions 1.9 adapted to be mechanically andelectrically secured upon the tapered end portions 13 of thefilament-mounting stems.

Each filament mounting portion 159 may be mechanically and electricallyconnected with the tapered end portion 18 of its corresponding supportstem by applying the end of the mounting portion 19 upon the taperedportion 13 of the stem .on which it is to be attached, wrapping a lengthof thread-like wire 20 about the pertions 13 and .13, and then securingthe portions 18 and 19 and the thread-like binding Wire 20 together byspot welding the same, as at 21.

in order to mount the filament supporting stems 1.7 and 17 accurately inposition extending coaxially with respect to the channels 15 and 15 tothereby accurately locate the position of the supported filament 11 inthe groove -14, the stems '17 and 17' may be received in preferablycylindrical mounting members 21 and 21 having portions adapted to extendsnugly Within the cavities 16 and 16', to thereby accurately locate thestems 17 and 17 with respect to the channels 15 and 15'. In theillustrated embodiment, the :stem :17 is insulated from the block 13,while the stem 17 is electrically connected with the block so that thefilament '11 may be energized for electron emission by-electricallyconnecting the .stem 17 and the block 13 with a suitable source offilament energizing power. It is, of course, within the contemplation ofthe present invention to electrically insulate both of the stems 17 and1.7 from the block 13, in which case it would become necessary toprovide means for connecting both of the stems with the filamentenergizing power source.

The mountin'gmember 21 preferably comprises a cylindrical body .ofinsulating material, such as magnesium oxide, lava, glass or porcelain,sized for snug intertitment at one end in the cavity .16. A cup-shapedshell 22, having an outstanding peripheral rim 23 and formed to snuglyreceive the portions of the insulating body 21 which extend outwardly ofthe cavity 16, is provided to support the member 21 inoperative-position on the block 13,, the shell being secured on theblock 1.3 in any preferred fashion and preferably by welding the rim 23to the block. The insulating body 21 is formed with an axial channel 24in coaxial alinement with the channel 15, and fitted with a preferablymetal sleeve 25 having a peened portion 26 at one end of the sleeve andformed with a peripheral head 27 medially thereof, whereby to secure thebody '21 on the sleeve 25 between the peened portion 26 and the head'27, the sleeve 25, at its end remote from the peened portion 26,extending outwardly of the insulating body through an opening 28 formedin the retaining member 22. The stem 17 and sleeve 25 are formed forsnug slidinginterfitment of the stem within the sleeve.

The cylindrical mounting member 21 may comprise a sleeve of electricalconducting material sized to snugly fit at one end within the cavity 16'and formed to snugly, yet 'slidingly receive the filament mounting stem17', the member 21' being secured in an suitable or preferred fashion onthe'block 13.

The sleeves 21" and 25 preferably comprise metal which may readily beweldingly connected with the stems 17 and 17'. .The sleeve 21' and theretaining shell 22 preferably comprise metal adapted to be readilyconnected, as by welding, with the'block 13. To this end, the sleeves21and 25 and the retaining shell 22 may be made of nickel or a ferrousalloy of nickel, which is readily connectible by welding either with thesteel block 13 or with the molybdenum filament mounting stems or both.

It will be seen from the foregoing that the emission element 11 auditssupport means, including the mounting stems 17 and 17, maybe readilyassembled on the block 13 with -the element 11 located in preciselydetermined position in the groove 14 with minimum effort andsubstantially without requiring the parts to he handled. To this end,the block '13may be placed face downwardly in a suitable holding fi turefor the reception of the stem mountings in the sockets 16am] 16'. Thestem mounting, comprising the insulating body 21, the retaining she] 22,and the stem mounting sleeve 25, may then be secured in place, as bywelding the rim 25 to the block 13; and the mounting, comprising themetal sleeve 21, may also be secured at one end in the socket 16'. Theblock 13 with attached stem mountings may then be inverted and securedin a suitable holder for the assembly of the stems "and 1.7 and.theemission element 11.

.If desired, theelement 11 may be mounted on the stems .17 and l7'before the same are assembled in the stem mountings. To this end, thestems 17 and 17 may be clamped :in desired spaced relation in a suitableholder and the element 11 attached to the stern ends 18 in the mannerheretofore described. 'lhereupon, the stems 17 and 17 may be applied inthe stem mountings by employing the holder to aid in applying the endsof the stems 17 and 17 remote from the filament carrying ends thereof,through the channels 15 and 15 and into the ends of the sleeves 21' and25. The stems may then be axially moved in the sleeves until the ends ofthe stems 17 and 17 which are remote from the filament carrying endsthereof, project outwardly of the sleeves 21' and 25, the stems 17 and17' at such stage of the assembly being straight rods ofsufficientlength to allow the same to be held in the mountings with thestem ends 18 projecting outwardly of the upper face of the block 13.

The holder may then be removed from the stems 17 and 17' to permit thesame to bedrawn through the sleeves 21 and 25, as by gripping the endsof the stems 17 and 17' which project from the block remote ends of thesleeves 21' and 25, in order to draw the filament supporting stem ends18 into the channels 15 and 15' to thereby support the filament inaccurately determined position within the groove 14. Thereupon, thesleeves 21' and 25 may be welded upon the stem portions enclosed thereinto secure the same against axial movement with respect to the block 13.After the welding operation, the stem 17 may be cut off opposite theblock remote end of the mounting sleeve 21, while the stem 17 may be cutoff at a desired distance outwardly of the mounting sleeve 25 and bentto form a connection lug 29, as shown in Fig. 1, for a purposehereinafter more fully described.

Alternately, the stems 17 and 17', prior to the attachment of theemission element 11 thereon, may be applied in the stem mountings inposition with their filament mounting ends 18 projecting above oroutwardly of the front face of the block 13. The emission element 11 maythen be mounted and attached to said ends of the stems, in the mannerheretofore described, after which the stems may be drawn axially in thesleeves 21 and 25 to the position shown in Figs. 1 and 2, and weldinglysecured in adjusted position in the sleeves in the manner mentionedsupra.

In order to mount the electron emission structure on and in an enclosingenvelope, such as the envelope of an X-ray tube, the same may besupoprted upon a pedestal or base 30 adapted to form a portion of theenclosing envelope. The pedestal 30, in turn, may carry a plurality ofmounting stems 31 and 32 secured thereon in spaced apart relationship,the stem 32 at least being relatively insulated electrically from theremaining stems 31. As shown, the pedestal 30 may comprise a tubularglass member 130 having a closed end 33, forming a pinch seal in whichthe stems 31 and 32 are embedded, with the stem 32 and at least one ofthe stems 31 extending through and on opposite sides of the pinch seal.

Alternately, the pedestal or base may comprise a tubular glass member130 having an end closed by means of a cup-shaped member 30' of metal,having a rim joined to the member 130' by a glass-to-metal seal. Thestems 31 and 32 may be mounted on the member 30' in any suitable orpreferred fashion in manner relatively insulating at least the stem 32from the metal member, as by means of a glass-metal seal 33. In suchcontraction, the stems 31, if desired, may be weldingly attached on themember 30, or they may be attached thereon as by means of glass-metalseals like the seal 33'. The stems 31 extend upwardly of the base 30 andhave outwardly offset upstanding end portions 31' remote from the basein position to supportingly engage the block 13, while the stem 32 isprovided with an offset lug 32' in position to register and engage withthe connection lug 29 of the stem 17, when the block 13 is in positionmountedon the stern portions 31'.

For the purpose ofmounting the block 13 upon the stern portions 31', theblock is provided with lateral grooves 34 which, for manufacturingconvenience, may

extend from one end of the block to its other end. These grooves areadapted to receive the stem portions 31' snugly therein; and a holdingcollar 35 may be applied snugly about the sides of the block 13 to holdthe stem portions 31 in the grooves 34, and hence mount the block 13upon the stems. To this end, the sleeve 35 is sized to tightly fit uponthe block 13; and the same may be welded upon the block, especially atthe stem portions 31', whereby to weldingly secure the stems in thegrooves 34 and to secure the sleeve 35 on the stems and on the block 13.When the block 13 is thus mounted on the stem portions 31, theattachment lug 29 will be disposed in adjacent contact with the lug 32',and said lugs are preferably mechanically and electrically securedtogether, as by welding.

In order to assemble and secure the block 13 upon the stems 31', theblock, with emission element 11 mounted and secured therein in themanner heretofore described, may be disposed face downwardly in asuitable jig or holder. The support 30, with stems 31 and 32 mounted inplace thereon, may then be applied to the block 13 in order to disposethe stem portions 31' in the grooves 34. The stem portions 31 may thenbe weldingly connected with the block 13; and the sleeve.

35 may be applied and weldingly or otherwise secured on the block 13,either prior to or after the assembly of the stern portions 31 in thegrooves 34.

It will be seen from the foregoing that the electronemission structuremay be built as a sub-assembly unit comprising the block 13 with theemission element 11 supported thereon, and the support base 30 includingthe tubular or skirt-like portions thereof. The entire structure may beassembled substantially without requir ing the handling or touching ofthe elements forming the cathode head. The glass skirt portions of thebase 30, of course, allow the same to be sealed in an envelope opening,such as is formed at an end of the envelope of a conventional X-raygenerating tube, to thereby form the base 30 as a re-entrant envelopeportion supporting the cathode structure in operative position withinthe X-ray generating tube.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the forms herein disclosed being preferred embodiments for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. An electron emitting cathode structure comprising a block of metalforming a head and provided with a groove opening upon the front face ofthe block, an elec.

tron emission element and mounting means for supporting the same on saidblock in position disposed in said groove, means forming a support base,and a plurality of supporting stems secured on and extending from saidbase, said stems being secured to said head to mount the same on thebase, at least one of said stems being electrically insulated from saidhead and comprising electrical conducting means connected with saidemission ele-.

ment for electrically energizing the same.

2. An electron emitting cathode structure comprisinga block of metalforming a head and provided with a groove opening upon the front face ofthe block, an electron emission element and mounting means forsupporting the same on said block in position disposed in saidgroove,vmeans forming a support base, and a plu rality of supportingstems secured on and extending from said base, said stems being securedto said head to mount the same on the base, at least one of said stemsbeing electrically insulated from said head'and connected with saidemission element for electrically energizing the same, said head beingprovided with lateral grooves for receiv-' ing others of said stems, andmeans for securing the stems in said lateral grooves.

3. An electron emitting cathode structure comprising a block of metalforming a head and provided with a groove opening upon the front face ofthe block, an electron emission element and mounting means forsupporting the same on said block in position disposed in said groove,means forming a support base, and a plurality of supporting stemssecured on and extending from said base, said stems being secured tosaid head to mount the same on the base, at least one of said stemsbeing electrically insulated from said head and connected with saidemission element for electrically energizing the same, said head beingprovided with lateral grooves for receiving others of said stems, suchgroove received stems being \veldingly secured to said -head in saidlateral grooves.

4. An electron emitting cathode structure comprising a block of metalforming a head and provided with a groove opening upon the front face ofthe block, an electron emission element and mounting means forsupporting the same 'on said block in position disposed in said groove,means forming a support base, and a plurality 'of supporting stemssecured on and extending from said base, said stems being secured tosaid head to mount the same on the base, at least one of said stemsbeing electrically insulated from said head and connected with saidemission element for electrically energizing the same, said head beingprovided with lateral grooves for receiving others of said stems, and asleeve-like collar secured on said head in position snugly embracing thesides thereof and overlying and enclosing the groove mounted stems.

5. An electron emitting cathode structure comprising a block of metalforming a head and provided with a transverse groove opening upon thefront face of the block and having opposite ends extending to andopening at the opposite sides thereof, a sleeve-like collar snuglyembracing the sides of and secured to said block in position enclosingthe opposite ends of said transverse groove, an electron emissionelement and mounting means for supporting the same on said block inposition disposed in said groove.

6. An electron emitting cathode structure comprising a cylindrical blockof metal forming a head, electron emission element supported on saidhead, a support base comprising a shell structure adapted forintegration in an envelope structure to form a part thereof, and meansfor mounting said block upon said base comprising a plurality ofmounting stems of electrical conducting rnaterial secured on andextending from said base, at least one of said stems being electricallyconnected with said emission element and insulated from said head, saidblock having spaced mounting grooves formed in its sides in position toreceive and to make mechanical and electrical connection with others ofsaid stems, and a collar snugly enclosing the sides of said block andcovering the stems in said mounting grooves, whereby the groove mountedstems may support said head on said base.

7. An electron emitting cathode structure comprising a cylindrical blockof metal forming a head, an electron emission element supported on andelectrically connected with said head, a support base comprising 'ashell struc-' ture adapted for integration in an envelope structure toform a part thereof, and means for mounting said block' upon said basecomprising a plurality of mounting stems of electrical conductingmaterial secured on and extending from said base, said block havingspaced mounting grooves formed in its sides in position to receive andto make mechanical and electrical connection with said stems, a collarsnugly enclosing the sides of said block and covering the stems in saidmounting grooves, whereby .the groove mounted (stems may support saidhead on said base with the stems electrically connected with said head,a connection stem secured on and extending from said base, insulatedmeans for mechanically securing said connection stem on and electricallyinsulating the same from said head, means for electrically connectingsaid emission element with said connection stem, and means extending onthe side of the shell structure remote from said head for electricallyconnecting said connection stem and at least one of said groove mountedstems with a source of emission element energizing power.

8. An electron emitting cathode structure comprising a block of metalproviding a head having front and back faces, said block being formedtherethrough with a pair of spaced channels opening upon the front andback faces of the block, an elongated electron emission element, supportmeans for mounting said element on said head in accurately determinedrelative position with respect to the front face of the head, saidsupport means comprising a pair of mounting stems of electricalconducting material extending 'coaxially in said channels, said emissionelement being mechanically and electrically connected on said stems inposition extending therebetwecn, and mounting means for securing a saidstem on said head comprising a mounting sleeve sized to snugly yetslidingly receive the stem therein, said sleeve comprising materialcapable of connection with a said stem by welding, whereby the stem maybe welded in accurately adjusted position in and axially of the mountingsleeve.

9. An electron emitting cathode structure comprising a block of metalproviding a head having front and back faces, said block being formedtherethrough with a pair of spaced channels opening upon the front andback faces of the block, an elongated electron emission element, supportmeans for mounting said element on said head in accurately determinedrelative position with respect to the front face of the head, saidsupport means comprising a pair of mounting stems of electricalconducting material extending coaxially in said channels, said emissionelement being mechanically and electrically connected on said stems inposition extending therebetween, and mounting means for securing a saidstem on said head comprising a mounting sleeve sized to snugly yetslidingly receive the stem therein, said sleeve comprising materialcapable of connection with a said stem by welding, whereby the stern maybe Welded in accurately adjusted position in and axially of the mountingsleeve, said head being formed with a seat in its back face, inconcentric relation with a said channel, for receiving the mountingmeans on said seat in position with said sleeve in coaxial alinementwith said channel.

10. An electron emitting cathode structure comprising a block of metalproviding a head having front and back faces, said block being formedtherethrough with a pair of spaced channels opening upon the front andback faces of the block, an elongated electron emission element, supportmeans for mounting said element on said head in accurately determinedrelative position with rcspect to the front face of the head, saidsupport means comprising a pair of mounting stems of electricalconducting material extending coaxially in said channels, said emissionelement being mechanically and electrically connected on said stems inposition extending therebetween, and mounting means for securing a saidstem on said head comprising a mounting sleeve sized to snugly yetsliding'ly receive the stem therein, said sleeve comprising materialcapable of connection with a said stem by welding, whereby the stem maybe welded in accurately adjusted position in and axially of the mountingsleeve, said head being formed with a seat in its back face, inconcentric relation with a said channel, and said seat being sized tosnugly receive an end of the mounting sleeve to accurately position thesleeve on the head.

'11. An electron emitting cathode structure comprising a block of metalproviding a head having front and back faces, said block being formedtherethrough with a pair of spaced channels opening upon the front andback faces of the block, an elongated electron emission element, supportmeans for mounting said element on said head in accurately determinedrelative position with respect to the front face of the head, saidsupport means comprising a pair of mounting stems of electricalconducting material extending coaxially in said channels, said emissionelement being mechanically and electrically connected on said stems inposition extending therebetween, and mounting means for securing a saidstem on said head comprising a mounting sleeve sized to snugly yetslidingly receive the stem therein, said sleeve comprising materialcapable of connection with a said stem by welding, whereby the stem,maybe welded in accurately adjusted position in and axially of the mountingsleeve, said head being formed with a seat in its back face, inconcentric relation with a said channel, a block of insulation sized tosnugly fit said seat and having an axial channel formed concentricallytherein, said channel being sized to snugly receive the mounting sleeve,means to secure said sleeve in said channel and means to secure saidblock of insulation on said head in said seat.

12. An electron emitting cathode structure comprising a block of metalforming a head provided with a groove opening upon the front face of theblock, said block being formed therethrough with a pair of spacedchannels opening in said groove and on the back face of the block, anelongated electron emission element, support means for mounting saidelement on said head in comprising material capable of connection withsaid stem by welding, whereby the stem may be welded in accuratelyadjusted position in and axially of the mounting sleeve, means forming asupport base for said cathode structure, a plurality of stem-likemembers forming support rods secured on and extending from said base,certain of said stem-like members being secured directly to said head tomount the same on the base, at least one of said stem-like members beingmechanically and electrically connected with one of said mounting stems.

References Cited in the file of this patent UNITED STATES PATENTS1,996,646 Juthe et a1. Apr. 2, 1935 2,200,115 Lessmann May 7, 19402,250,323 Atlee July 22, 1941 2,471,298 Atlee May 24, 1949

